There is known the process for producing (meth)acrolein or (meth)acrylic acid, which comprises the steps of feeding a raw material of the (meth)acrolein or (meth)acrylic acid, and a molecular oxygen-containing gas mixed with a diluting gas and compressed by a compressor, to a oxidation reactor to conduct a catalytic gas-phase oxidation reaction therebetween; feeding the obtained reaction gas to an absorption column to contact with water; recovering an aqueous solution of the (meth)acrolein or (meth)acrylic acid from a bottom of the absorption column and an exhaust gas from a top of the absorption column; and recycling a part or whole of the thus recovered exhaust gas to reuse as the diluting gas (for example, Japanese Patent Application Laid-open (KOKAI) No. 2001-220362).
In the above conventional process, the diluting gas has been used to prevent the composition of raw gas obtained by mixing the raw material of (meth)acrolein or (meth)acrylic acid with the molecular oxygen-containing gas from falling within a range of explosion thereof.
The exhaust gas recovered from a top of the absorption column contains aldehydes, acetic acid, terephthalic acid as a sublimatable substance, etc., which are by-produced by the catalytic gas-phase oxidation reaction, as well as a considerable amount of the (meth)acrolein or (meth)acrylic acid and water. Therefore, low-boiling components such as aldehydes contained in the exhaust gas tend to be condensed and solidified by polycondensation reaction thereof. The thus produced solids tend to be deposited in conduits of the reactor, finally resulting in clogging thereof.
To solve these problems, the above Japanese Patent Application (KOKAI) has proposed the method of heating the exhaust gas used as the diluting gas to a temperature not less than the same temperature as that of a top gas of the absorption column.
The above method can be effective to prevent clogging in conduits, etc., disposed on an upstream side of the position where the exhaust gas and the molecular oxygen-containing gas are mixed with each other. However, since the molecular oxygen-containing gas is usually used in a relatively large amount as compared to the exhaust gas, the temperature of the exhaust gas decreases subsequent to mixing with the molecular oxygen-containing gas, thereby failing to sufficiently prevent the conduits, etc., from clogging. In particular, the compressor tends to suffer from problems such as clogging or damage.
Accordingly, an object of the present invention is to provide a process for producing (meth)acrolein or (meth)acrylic acid, which comprises the steps of feeding a raw material of the (meth)acrolein or (meth)acrylic acid, and a molecular oxygen-containing gas mixed with a diluting gas and compressed by a compressor, to a oxidation reactor to conduct a catalytic gas-phase oxidation reaction therebetween; feeding the obtained reaction gas to an absorption column to contact with water; recovering an aqueous solution of the (meth)acrolein or (meth)acrylic acid from a bottom of the absorption column and an exhaust gas from a top of the absorption column; and recycling a part or whole of the thus recovered exhaust gas to use as the diluting gas, which process is capable of preventing the compressor from suffering from clogging or damage.